The present invention relates to improved modified asphalt characterized by better binding of the modifier material to the asphalt.
The addition of polymers to asphalt improves the physical and mechanical properties of the asphalt. The most commonly used polymers are styrene butadiene styrene (SBS), styrene butadiene (SB) and styrene butadiene rubber (SBR). Polymer modified asphalts (PMA) are used in pavement and roofing materials. Modified asphalts and asphalt emulsions are primarily produced through conjugated-diene backbone type polymers.
A number of techniques are currently used to link polymers with asphalt. One technique is to use asphalt binders. However, such binders do not meet all of the requirements developed by the SUPERPAVE protocol. Inferior binders result in damage to asphalt pavement including permanent deformation, thermal cracking and flex fatigue. These damages diminish the life of the pavement.
Another linking technique uses additives to assist with coupling the polymer modifier material to asphalt molecules to produce polymer modified asphalts. These coupling additives include alkyl polysulfide, poly phosphoric acid, dithio, carbamates, phosphorous, penta-sulfide, 4-4′-dithiomopholine, furfural, thiozole derivatives, phosphorous pentoxide, hydrogen peroxide, sodium hydroxide, sulfur trioxide.
A major drawback of conventional polymer modified asphalts is that the asphalt develops a gel in certain portions thereof resulting from over-reactivity of the linking or activator material. This is particularly the case where polymer modified asphalt is stored prior to installation. Gel formation makes the polymer modified asphalt difficult to work with and install. Additional drawbacks include separation between the top and bottom of the polymer modified asphalt, as well as reduced elastic recovery.